Flexible corrugated multilayer metal foil shields and method of making

ABSTRACT

A flexible multilayer metal structure includes using multiple layers interlocked to form folds holding the layers together. These folds can extend into non-edge portions of the multilayer structure so that the multilayer structure defines air gaps that aid in producing a heat-shielding effect.

This application is a continuation of application Ser. No. 08/871,771,filed Jun. 9, 1997 now U.S. Pat. No. 5,939,212.

FIELD OF THE INVENTION

This invention relates to multilayer metal foil and metal sheetstructures which have utility as heat shields and as acoustic shields.

BACKGROUND OF THE INVENTION

Multilayer metal foil insulation has been used for many years, asillustrated by U.S. Pat. No. 1,934,174. Such metal foil insulation hastypically been used in high temperature applications for reflective heatinsulation. In those applications, the layers of metal foils areembossed to provide separation between the layers, and the stack oflayers are protected in a container or rigid cover to prevent the stackof metal foils from becoming compressed at any portion, which woulddecrease the heat insulation value of the stack.

U.S. Pat. No. 5,011,743, discloses that multilayer metal foil insulationcan provide enhanced performance as a heat shield when a portion of themultilayer metal foil is compressed to provide a heat sink area throughwhich heat is collected from the insulating portions of the stack anddissipated from the heat shield. Such multilayer metal foil heat shieldsare formed from a stack of embossed metal foil layers by compressingportions of the stack to create the desired heat sink areas. The layersare attached to each other or stapled together to prevent the layersfrom separating. The heat shields and acoustic shields formed accordingto the disclosure of the U.S. Pat. No. 5,011,743 are typicallycompressed in the heat sink areas and cut to a desired pattern. Suchmultilayer metal foil heat shields do not normally have sufficientstructural strength for stand-alone use in many applications. For manyapplications, the metal foil heat shields are typically attached to astructural support member or pan to provide a final assembly which isthen placed in service as a heat shield or acoustic shield. The supportmembers are typically metal pans, metal stampings or metal castings.Typical applications for such heat shield assemblies include automotiveheat shield applications.

The disclosures of the above patents are incorporated herein byreference.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a multilayer metal foilinsulation structure which is flexible and suitable for use in heatshield and acoustical shield applications.

The flexible corrugated multilayer metal foil structure according tothis invention comprises a stack of metal foil layers which are formedin corrugations extending across a stack of the metal foil layers,wherein all of the layers have the same corrugated pattern and shape asa result of the stack being shaped in corrugations or the layers beingseparately shaped in corrugations then nested into a stack. A portion ofthe corrugations of the stack of metal foil layers is compressed to foldthe layers together whereby the layers are interlocked together inoverlapping relationship. The resulting multilayer corrugatedinterlocked structure is flexible by means of the ability of themultilayer corrugated interlocked structure to flex along the valleys orpeaks of the corrugations where they are not compressed and folded andalong the valleys between the corrugations where the peaks of thecorrugations are compressed and folded to interlock the layers together.Depending on the thickness of the layers, number of layers and thedegree of compression of the interlocked layers, the compressed portionsof the corrugations can also flex along with the uncompressed portionsof the interlocked structure.

The flexible corrugated multilayer metal foil structures of thisinvention comprise at least three metal layers at least two of which aremetal foil layers having a thickness of 0.006 in. (0.15 mm) or less. Itis generally preferred that the flexible corrugated multilayerstructures of this invention contain at least three layers of metal foiland more preferably will typically contain five or more layers of metalfoil. Preferably, the metal foil layers will be 0.005 in. (0.12 mm) orless, with 0.002 in. (0.05 mm) metal foil being a preferred thickness,especially for the interior layers of the flexible corrugated multilayermetal foil structure. In addition to the layers of metal foil, optionalprotective exterior layers of metal sheet on one or both sides of theflexible corrugated multilayer structure can be included. Such metalsheets have a thickness greater than 0.006 in. (0.15 mm) and up to about0.050 in. (1.27 mm). The thickness of the optional exterior protectivemetal sheet is selected such that it can be corrugated into the sameshape and pattern as the other layers (either separately then nested, orsimultaneously corrugated as part of the stack) and compressed intointerlocking engagement with the other layers as part of the unitarymultilayer metal foil structure according to this invention. Preferably,the protective exterior metal sheet layer will be between about 0.008in. (0.20 mm) and about 0.030 in. (0.76 mm). One preferred flexiblecorrugated multilayer metal foil structure according to this inventionis made entirely of metal foils each having a thickness of 0.006 in. orless without the use of heavier external sheet layers.

One or more of the individual metal foil layers comprising part of themultilayer structure of this invention may be embossed or contain otherspacers to provide spaces and gaps between the layers. Even though someof the embossments or gaps may be reduced during the formation of thecorrugations of the multilayer stack and some may be entirely eliminatedin those areas where the corrugations are compressed to form the foldsinterlocking the layers together, the residual spaced apart gaps betweenthe layers in various parts of the multilayer corrugated structure isadvantageous in many applications with respect to the heat and acousticinsulating and shielding properties. However, without embossments orother spacers to hold the layers apart, the metal foil layers willinherently have some gaps and spaces between the layers due to wrinklesor other deformations that inherently occur during the formation of thecorrugations of the multilayer metal foil structure. In addition tospacers in the form of embossments or wrinkles in the layers themselves,separate spacers may be used to provide gaps between the layers, such ascompressible foil pieces or mesh, or non-compressible materials, so longas the presence of such spacers does not interfere with the compressionand folding of the corrugations together at desired locations in thestructure to interlock the layers and prevent separation of the layerswhen the multilayer metal foil structure is used for its intended use.

The flexible multilayer corrugated metal foil structures of thisinvention, when formed with corrugations across the stack of layers, arerigid or at least resist bending in one direction but are flexible inthe other direction due to the ability of the stack to flex along thepeaks and/or valleys of the corrugations. This flexibility of themultilayer corrugated structure enables application thereof as heat andsound shields to contoured shapes, especially curved planar surfacessuch as conduits. However, the multilayer corrugated structures of thisinvention can also be fitted or formed into or onto any shape desired byflexing the multilayer structure in one direction along the corrugationsand by bending, creasing or buckling the corrugation ridges to shape thestructure in the other direction across the corrugations. In addition,the spacing of the corrugations can be laterally stretched out orcompressed together to assist in shaping the multilayer corrugated metalfoil structure to fit desired three dimensional shapes. For example, ashield can be formed to a desired shape by forming the corrugations inthe stack of metal foil layers, shaping the stack including stretchingor compressing the corrugations laterally (along the plane of the layer)as needed for shaping, then compressing the corrugations verticallywhere desired to fold the corrugations and interlock the layerstogether.

In an optional structure, the corrugated multilayer metal foil structureof this invention can be made flexible in the other direction bycompressing creases across the corrugations, whereby the creases arecompressed deeply enough into the corrugations to provide the bendingand flexing of the multilayer structure along those creases. It will berecognized that in the formation of such creases to provide additionalflexibility to the corrugated multilayer metal foil structure of thisinvention, the compression to form the creases will also provide theadditional function of folding the corrugated layers and interlockingthe layers together with one another in the same fashion as the abovedescribed vertical compression of the corrugations to interlock andprevent separation of the layers. This folding and interlocking of thelayers by the creasing can be in addition to or instead of the firstcompression of the corrugations mentioned above to fold and interlockthe layers. Such creases can be any desired width, from a knife-edgesharp crease to wide flattened strip across the corrugations, and can beany desired direction across the corrugations depending on theflexibility and the heat or sound shielding properties desired in thefinal product.

The present invention provides a method of forming a flexible corrugatedmetal foil structure by first providing a stack of metal foils. Eachmetal foil layer optionally may be individually embossed, wrinkled,corrugated (for example, very small corrugations in period or heightcompared to the main corrugations of the multilayer product) or containother spacers to provide gaps between the layers. The stack of metalfoils is then shaped as a unitary structure into corrugations, which maybe done using conventional metal corrugating methods and equipment.After the corrugations are formed in the multilayer stack, a portion ofthe corrugations are compressed to fold the layers over each otherwhereby the layers are interlocked together. The interlocking of thelayers prevents separation of the layers while retaining the flexibilityof the multilayer metal foil corrugated stack along the corrugations byflexing along the peaks and valleys or channels of the corrugations. Theportion of the corrugations which are compressed in order to fold andinterlock the layers may be any portion or area of the corrugationsdesired for a particular product, but sufficient to prevent separationof the layers during handling and use. For example, in many applicationsit will be preferred that the edges of the corrugated stack becompressed whereby the metal foil layers are folded and interlockedaround the perimeter or along at least one edge of the multilayercorrugated metal foil stack. Other configurations may be desirabledepending on end use of the multilayer metal foil structure. Forexample, it may be desired to compress an interior portion of thecorrugations in a strip parallel with the edge of the multilayer stripwhereby the layers are folded and interlocked together in an interiorportion of the corrugated multilayer metal foil structure leaving theedges uncompressed in the corrugated configuration. Alternatively, itmay be desired to substantially compress periodic or alternatingcorrugations along all or most of the length of each individualcorrugation, whereby a certain proportion of the corrugations arecompressed to fold and interlock the layers together while the entirelength of other corrugations remain uncompressed.

The shape of the corrugations can be selected by one skilled in the artdepending on the desired properties of the structure. For example, thecorrugations may be sinusoidal, square, rectangular, semicircular orother appropriate corrugation shape. The size, height, width and spacingof the corrugations can be uniform and regular, or can be nonuniform andirregular, so long as the corrugations are designed so that when theselected portion of the selected corrugations are compressed, the layerswill readily fold and interlock together as a result of the compressionof the corrugations. Similarly, the shape of the folds into which thelayers are deformed and locked together can be selected and designeddepending on the interlocking properties desired in the final flexiblecorrugated multilayer metal foil product produced according to thisinvention.

The flexible multilayer metal foil structures of the present inventionhave a wide range of utilities, but are preferred for heat andacoustical shielding applications, particularly in automotive use. Theflexible multilayer metal foil structures of this invention have utilityas heat insulating materials, but are preferred for use in heatshielding applications for spreading and dissipating heat from pointsources of heat, or hot spots. Due to the high lateral conductivity ofthe multiple metal layers, heat can be efficiently conducted laterallyfrom a hot spot to other locations within the flexible multilayer metalfoil structure where the heat can be absorbed by or dissipated intosurrounding environment where the temperature is lower than in the areaof the hot spot heat source. It will be expected that in the corrugatedmultilayer metal structure according to the present invention, heat willbe most readily and rapidly conducted along the shortest conductivepath, which is along the length of the channels of the corrugations.Heat will be conducted more slowly in the direction transverse to thecorrugation channels, i.e., along or across the peaks and valleys of thecorrugations. Heat will also be conducted more rapidly along the pathsresulting from the compressed areas and the creased areas referred toabove, where the peaks and valleys of the corrugations have beenessentially flattened. Given these properties, one can readily designcorrugated multilayer metal foil heat shielding structures according tothe present invention to shield and insulate hot spot sources of heat byconducting and dissipating the heat laterally along the corrugations indesired and specific directions. Similarly, the flexible multilayermetal foil structures of this invention have utility as acousticalshields due to the vibration and sound absorbing properties of thecorrugated multilayer metal foil structure. For acoustic applications,it will be apparent to one skilled in the art that it may be desirableto have alternate material layers in between the corrugated metallayers. Materials such as plastic films, adhesives, fibers and othermaterials may be used to enhance the acoustic damping properties of themultilayer corrugated metal foil structure, although some of thosealternate materials may not be suitable for use in some heat insulationor heat shielding applications.

The corrugated multilayer metal foil structure of this inventionprovides two advantages for utilization of the structure in various heatand acoustic shielding and insulating applications. First, theflexibility provided by the corrugations provides convenience inpositioning the flexible corrugated multilayer metal foil structure ofthis invention in desired applications. As will be recognized, theadditional flexibility by providing the above-referenced longitudinalcreases across the corrugations provide additional flexibility, or thepreforming the corrugated stack of metal foil layers before interlockingthe layers together, will enable one to utilize the structures of thisinvention where various shapes of heat or acoustic shielding arerequired. The second property provided by the corrugated multilayermetal foil structure of this invention is the surprisingly high verticalstrength and load bearing capability of the flexible corrugatedmultilayer metal foil structure formed according to this invention.After the selected portions of the corrugations are compressed to formthe folding and interlocking of the layers together, the remaininguncompressed portions of the corrugations will support vertical loadsand exhibit resistance to compression higher than one would expect formetal foils. Such load bearing properties make the flexible corrugatedmultilayer metal foil structures of this invention particularly usefullyas heat and acoustic shields under the carpet in passenger compartmentsof vehicles. The corrugated multilayer metal foil structures accordingto this invention may be positioned between the floor pan of anautomobile and the passenger compartment carpet to absorb and dissipateheat from hot spot sources underneath the floor pan, such as a catalyticconverter or exhaust systems, and to absorb and dampen noise, such asroad noise. The corrugated shape of the multilayer metal foil structuresof this invention provides sufficient resistance to compression andcrushing under the carpet to enable the corrugated metal foil structureto maintain its corrugated shape and its heat and acoustic shieldingproperties under ordinary usage where vertical loads are applied to thecorrugated multilayer metal foil structures by passengers stepping onthe carpet.

It will be recognized by one skilled in the art that the flexiblecorrugated multilayer metal structures according to this invention canbe formed with metal sheets having thicknesses greater than 0.006 in.and without the use of metal foil layers having a thickness of 0.006 in.or less. Such flexible corrugated multilayer metal sheet structures areformed in the same way as the multilayer metal foil structures and maybe desirable for additional strength and vibration resistance in certainend use applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a multilayer metal foil stack which isformed into corrugations.

FIG. 2 is a partial perspective view of an edge portion of the stack ofcorrugated metal foils illustrating the compressed corrugations wherebythe layers are folded and interlocked together.

FIG. 3 is a cross section view of an alternate shape of the folding andinterlocking of the layers by compression of the corrugations.

FIG. 4 is an illustration of additional creasing of the corrugations toprovide flexibility in the longitudinal direction across thecorrugations, as well as the lateral direction along the corrugations.

FIG. 5 is a perspective view illustration of a diagonally embossedmultilayer metal foil strip utilized for conduit insulation.

FIG. 6 is an illustration of the application on the corrugatedmultilayer metal foil structures of this invention to a vehicle.

DESCRIPTION OF THE INVENTION

This invention adapts metal sheet corrugation forming processes toprovide novel flexible, corrugated multilayer metal foil and metal sheetstructures. Conventional metal corrugation forming processes, such asdisclosed in U.S. Pat. Nos. 3,966,646 to Noakes et al. and 4,810,588 toBullock et al., incorporated herein by reference, may be adapted for usein forming the corrugations utilized in the multilayer metal foilstructures of this invention. While Bullock et al. is directed tonon-nesting corrugated metal foil layers, it is apparent that thecorrugation processes similar to Noakes et al. and otherwise known inthe art can be adapted to form the corrugations in the multilayer metalfoil structures of the present invention. In the practice of the presentinvention, it is preferred that a stack of metal foils and metal sheetsfirst be provided in the desired number of layers, wherein the layersmay contain embossments or other spacers for providing desired gaps orseparation between the layers. The stack of metal foils is thencorrugated as a unitary structure to form corrugations in all of thelayers of the stack simultaneously. The corrugated stack of metal foilsis then subjected to compressing selected areas or portions of thecorrugations to cause the layers in the stack to fold over each otherand interlock together as the corrugations are compressed to anessentially flattened condition in the selected areas. The resultingproduct provided by this invention is a multilayer metal foil structurewherein all of the layers are folded and interlocked together in thosecompressed portions of the corrugations, which holds the entirestructure together, and the multilayer metal foil structure remainsflexible due to the bendability in the areas of the peaks and/or valleysof the corrugations.

In an alternative method of forming the structures of the presentinvention, individual metal foil layers and metal sheet layers may becorrugated separately, then stacked together and nested as a stack ofpre-corrugated individual sheets. The corrugations can be regular orirregular in shape, period, etc., so long as each of the sheets willsubstantially nest with the other sheets to enable the compression andfolding of the stack of corrugations for the interlocking of the layerstogether. The nested stacks of corrugated sheets can then be subjectedto compression of portions of the corrugations to fold and interlock thelayers together to form the corrugated multilayer metal foil structuresof this invention. One or more of the individual layers may be embossedor otherwise dimpled, crinkled, corrugated (in a non-nesting directionor pattern different than the adjacent layers) or otherwisetopographically contoured in order to provide gaps and spacing betweenthe layers. When metal foils are provided with such embossments orspacers to provide gaps, it will be recognized that a portion of theembossments or spacers will usually be eliminated or at least diminishedduring the corrugation process to form the corrugated multilayer metalfoil structure according to this invention. It will also be recognizedthat when portions of the corrugations in multilayer preform stacks arecompressed to fold and interlock the layers together, the embossments orother spacers may be substantially or entirely eliminated in thosecompressed areas. However, in many applications it may be desirable toprovide such embossments or spacers to form gaps between the layers,because gaps between the layers in the corrugated areas, which are notcompressed and interlocked together, generally enhance the heat andsound insulating and shielding properties of the flexible corrugatedmultilayer metal foil structures of this invention.

This invention is further illustrated by reference to the drawings. FIG.1 illustrates a stack (10) of metal foil sheets (1) which are corrugatedin the form of a stack of sheets to form corrugations (2) laterallyacross the stack of sheets. One or more of the sheets can have optionalembossments (7) preformed therein to provide preferred gaps orseparation between the layers of sheets (1). The corrugations can bedesigned and selected to have any shape, sinusoidal, semicircular,square, rectangular, etc., which is appropriate to provide useablecorrugations which can be compressed to fold and interlock the metalsheets together as provided by this invention. The height of thecorrugations and the period or distance between the corrugationslikewise can be selected by one skilled in the art depending on theproperties desired in the final products and depending on the economicsand equipment available for forming the corrugations in the stack. Thecorrugations can be formed in the stack of metal sheets by conventionalmetal corrugating methods and equipment, such as illustrated in U.S.Pat. No. 3,966,646 referred to above. It will also be recognized by oneskilled in the art that each sheet can be corrugated separately, thenthe corrugated sheets stacked and nested to form the stack of corrugatedmetal sheets useful in this invention. Similarly, one can form a stackof metal foils, such as four layers of 0.002 in. metal foils andcorrugate that stack of metal foils. Separately, one can corrugate asingle cover sheet such as a 0.010 in. thick sheet then place thecorrugated cover sheet on and nest the cover sheet with the stack ofcorrugated metal foils to produce the corrugated multilayer metal foilstack useful in forming the structures according to this invention. Itwill also be recognized that it is not required or necessary in thecorrugated multilayer metal foil and sheet structures of this inventionfor all layers to be nested throughout the structure. For interlockingof the layers by compressing stacks of corrugations, the layers need tobe nested at those points, but it may be desirable to provide portionsor areas of the structure where the corrugations in the layers do notnest. Such a configuration of the product of this invention may bedesired where additional total height is desired for insulation valuesor other purposes.

FIG. 2 is a partial perspective view of the edge of the corrugated stackof metal sheets of FIG. 1 showing how the compression of thecorrugations (2) folds and interlocks the layers together. In thisillustration, the corrugations are compressed in edge area (5) into anomega (Ω) shape in areas (26) which folds the layers together andinterlocks the layers in the stack. Other shapes of folds can be used,such as “T”, “L” or mushroom shapes. This type of compression of thecorrugations can be performed along the edge of the stack as illustratedor in an interior portion of the stack, or both, as desired to providesufficient interlocking of the layers to prevent separation of thelayers during use of the final product. FIG. 2 illustrates the optionalembossments (7) remaining in the corrugated areas and providingseparation of the layers and the flattened embossments (7 a) in the area(5) where the corrugations have been compressed. Reference to FIG. 2also illustrates the properties of the multilayer metal foil structureof this invention. The flexibility of the structure is provided by themultilayer corrugated interlocked structure being able to flex intransverse and longitudinal directions, such as along valleys (24)between corrugations (2) and at the peaks (23) of corrugations (22) dueto the transition between the peaks and the flattened areas (26) of thecorrugations can also flex to some extent when the structure is bent.

FIG. 3 illustrates in cross section view another shape of folding andinterlocking of the layers together by the compression of a portion ofthe corrugations. The corrugations of the multilayer stack arecompressed to form flattened areas (36) to fold and interlock thelayers. Valley areas (34) remain between the compressed portions ofcorrugations and the uncompressed portions to provide flexibility of thefinal corrugated structure having interlocked layers. While two examplesare shown, other shapes of folding and interlocking of the layerstogether to form the flexible integral structure according to thisinvention will be apparent to one skilled in the art following thedisclosure herein.

FIG. 4 also illustrates an additional embodiment of the flexiblecorrugated multilayer structure of this invention wherein parallelcorrugations (42) extending transversely across the stack of sheets arecompressed at edge area (46) and are creased by longitudinally extendingcreases (44) which, together with corrugations (42), provide the abilityof the multilayer structure to bend and flex along creases (44) or alongthe valleys between corrugations to provide additional shapability ofthe corrugated multilayer metal foil structure of this invention.Creases (44) can extend at any angle across the corrugations as desiredfor the flexibility and shapability to be designed into the product.

FIG. 5 illustrates additional embodiments of this invention wherein thecorrugations (52) are formed at a right angle or at an oblique angleacross the width of the stack of metal foils with the corrugationscompressed at edge areas (56) to interlock the layers together. Theangled configurations of the corrugated multilayer metal foilinterlocked structure of this invention can wrapped in repeatingsections (the right angle version) or can be spiral wrapped (the obliqueangle version) around a hot, cold or cryogenic conduit (58) where themultilayer stack flexes at the valleys or peaks of the corrugations inthe structure to facilitate the wrapping of the multilayer structure ofthis invention around a conduit and corrugations (52) are positionedparallel with the axis of the conduit.

FIG. 6 is a schematic illustration of the application of a shieldillustrated in FIG. 4 to the underbody section of a vehicle (60). Shield(41) can be applied to the underneath surface of the passengercompartment pan or floor (61) by mechanical attachment or by adhesiveattachment. It is also to be understood that a shield, such as shield(41) from FIG. 4 as well as any desired shape of corrugated multilayermetal foil shield, can be designed and formed according to thisinvention to fit any desired portion of the underbody of a vehicle, orthe fire wall or other area of the engine compartment, etc. of avehicle. The shields made according to the present invention areadvantageously attached to the portions of the vehicle by adhesive orother mechanical attachment in order to provide an integral body orchassis part, because the efficient, light-weight, recyclable shields ofthis invention can be designed to provide a desired combination of heatshielding and acoustic shielding at any desired location on the vehicle.It is also to be recognized that the direct attachment by mechanical oradhesive attachment of the multilayer metal foil shields of thisinvention to the desired areas and components of a vehicle is enabledand made possible by the flexibility of the corrugated multilayer metalfoil shields and parts made according to the teaching of this invention.

The compression of the corrugations to fold and interlock the layerstogether can be performed as desired by one skilled in the art. Apreferred method and apparatus for compressing the corrugations is theuse of a compression tool, such as a resilient, e.g., rubber or plastic,member which can compress the corrugations to fold the corrugations inthe omega, “T”, “L”, mushroom or other shape to interlock the layers.One advantage of using a rubber compression member is that thecorrugations are sufficiently compressed to fold and interlock thelayers together but the compressed areas to remain somewhat moreflexible than would occur if the compressions are flattened under moreextreme pressure. Alternatively, metal, plastic, wood or othercompression members may be used to accomplish the compression of thecorrugations to fold and interlock the metal foil layers of the stacktogether. As referred to above in FIG. 4, the longitudinal creases whichcan be compressed across the corrugations to provide flexibility of themultilayer structure can likewise be formed using any desired method andcompression member. As will be recognized by one skilled in the art thecompression member may be a flat member, a V-shaped member or a knifeedge type member, depending on the type of compression and, in the caseof the longitudinal creases across the corrugations, the flexibilitydesired in the final product. The compressed portions of thecorrugations to fold and interlock the layers together can be at anydesired location or locations, such as at the edge of the multilayerstructure or in an interior portion of the multilayer metal foilstructure. As will be apparent to one skilled in the art, anycombination or configuration of compressed areas to provide theappropriate folding and interlocking of the layers for a particularproduct design can be carried out following the teachings of thisinvention. The edge portion of the multilayer structure may be left openin the corrugated uncompressed condition when desired, and interiorportions of the corrugations compressed to interlock the layerstogether. Alternatively, the edge portion in addition to beingcompressed can also be folded, rolled, curled, crimped or shaped in anydesired pattern. A folded or crimped edge in some applications will beuseful for providing a site for mounting hardware, when attaching themultilayer structure to, for example, the underbody of a vehicle. Thus,it is apparent that in addition to the compression of the corrugationsto fold and interlock the layers, the layers may also be attached byother methods, such as stapled, clipped or bolted to other structuralmembers for end use applications.

The materials useful in the corrugated stacks of this invention willlikewise be apparent to one skilled in the art and will includetypically aluminum, stainless steel, copper, similar metal foils andmetal sheets, plastic coated metal foils and sheets, laminates ofmetals, alloys of these and other metals, and metallic materials whichare plastically deformable and are permanently deformable. In additionto metal, other materials may be interlayered between two or more of themetal foil layers of the multilayer structure of this invention. Forexample, plastic films, adhesive layers, spray on adhesives, coatings,etc. may be included between the metal foil layers, particularly inacoustic applications where additional sound damping is desired. Thethickness of the various metal and other layers employed will depend onthe end use application. It is preferred that the multilayer structurebe made primarily of metal foils having a thickness of 0.006 in. or lessand in particular it is preferred that in, for example, a five layerstructure, at least the three interior layers are thin metal foils, forexample 0.002 in. thick metal foils. The exterior layers of an all-foilstructure are frequently desired to be heavier metal foils of 0.005 in.or 0.006 in. in thickness. Likewise, when the exterior layers aredesired to be protective layers, they may be metal sheets of 0.010 oreven up to 0.050 in. in thickness. In this regard, it is also recognizedthat the flexible corrugated multilayer metal structures of thisinvention can be a non-foil structure made entirely of layers of metalsheets thicker than metal foils, i.e., metal sheets having thicknessesin excess of 0.006 in. For example, flexible corrugated multilayer metalstructures according to this invention can be made using five layers of0.010 in. thick metal sheets.

The number of layers and the thicknesses of each layer will be selectedby one skilled in the art depending on the flexibility desired, thevertical strength required in the final corrugated flexible product, thecapacity for lateral heat transfer, the requirements for sound damping,etc. The thickness of various metal foil layers will vary from 0.0008 to0.006 in., with the 0.002 in. and 0.005 in. metal foils being preferredfor many applications. When heavier sheets are used and in particularfor the top sheets or protective exterior sheets, the metal sheets canhave a thickness of greater than 0.006 in. up to about 0.050 in., withthe preferred top sheets or exterior sheets having a thickness of 0.010in. to about 0.030 in. Some examples of combinations of number of layersand thicknesses of the layers used in forming the flexible corrugatedmultilayer metal foil structures of this invention are: (in mils, 1mil=0.001 in.) 10/2/2/2/5; 5/2/2/2/5; 8/2/2/2/4; 10/2/2/10; 5/2/2;5/0.8/0.8/5; and 10/2/0.8/0.8/2/5. Examples of non-foil metal sheetstructures are: 10/8/8/8; 30/10/10/10/30; 8/8/8; and 50/8/8/10. Thematerials useful in this invention are similar to those disclosed incopending patent application Ser. No. 08/871,275 filed Jun. 9, 1997, thedisclosure of which is incorporated herein by reference.

The total thickness of the corrugated multilayer metal foil/metal sheetstructures of this invention can be designed and selected by one skilledin the art to meet the requirements for heat or sound shielding. Forexample, a typical under carpet application can utilize a structure of10/2/2/5 mil layers with corrugation heights to give the structure atotal vertical thickness of about 3 mm to about 4 mm from the base tothe top of the corrugations.

As discussed above, the flexible corrugated multilayer metal foil andmetal sheet structures of this invention are useful for heat insulationand dissipation and acoustic shielding. In these applications thestructures of this invention can be manufactured in any desired shapeand configuration for any application desired. For example, thesestructures can be designed and adapted for use on hot exhaust conduitswhen wrapped as illustrated in FIG. 5; they can be made in large shapedsheets which will conform to the shape of the underneath side of avehicle passenger compartment floor pan or can be made to conform to theshape of a vehicle fire wall. In these applications, the structures ofthis invention serve both to insulate and to laterally conduct andspread heat from hot spot heat sources to the cooler areas where it canbe absorbed by or dissipated to the environment adjacent to themultilayer metal structures of this invention. The flexible corrugatedmultilayer metal foil structures of this invention likewise can beplaced, as discussed above, under the passenger compartment carpet ofvehicles to spread and dissipate heat from the areas where the exhaustand catalytic converter systems tend to heat the floor pan of thepassenger compartment. Such applications also provide acousticinsulation as well. Attachment of the flexible corrugated multilayermetal structures of this invention will be apparent to one skilled inthe art using ordinary mechanical attachments such as clips, bolts,screws and the like. Adhesive attachment, for example by masticcoatings, etc., is a preferred method for placing the structures of thisinvention on various vehicle or automotive applications, especially forunderbody applications, e.g., on the bottom of the floor pan of thepassenger compartment. The corrugated multilayer metal foil and metalsheet structures of this invention may also be laminated to or betweenother materials such as metal, fabric, plastic, etc., when desired inparticular applications and service conditions. For example, thecorrugated multilayer structures of this invention can have a smoothlayer of metal foil or metal sheet or an embossed, non-corrugated metalfoil or metal sheet on one or both sides of the structure, attached byadhesive or by mechanical attachment to provide desired structuralstrength or shielding properties. Other non-vehicle and non-automotiveutilities for the structures of this invention will be apparent to oneskilled in the art, such as liners for ovens, etc. In various acousticend use applications, it may be desirable to form perforations in one ormore layers in the structure to enhance the sound and vibrationabsorbing capacity of the structure. Such perforations can be formed inconjunction with embossments, for example a perforations can be made atthe points of embossments in metal foils. Or, such perforations can beformed in rows along the top ridges of the corrugations in some or allthe layers of the structure.

Other variations of the methods of making and the structures of thepresent invention as well as end use application designs will beapparent to one skilled in the art following the teachings of thisinvention.

We claim:
 1. A flexible multilayer metal structure suitable for use as aheat shield comprising: metal layers, at least two of the metal layersbeing metal foil layers each having a thickness of 0.006 in. or less;wherein the layers being interlocked together to form a number of foldsof the layers, the folds holding the layers together, at least some ofthe folds extending into non-edge portions of the multilayer metalstructure, wherein the multilayer structure defines air gaps that aid inproducing a heat shielding effect.
 2. The flexible multilayer metalstructure of claim 1 wherein the metal layers are corrugated and nestedtogether in a stack, and the compressed to interlock the layerstogether.
 3. A flexible multilayer metal structure according to claim 2wherein the corrugations are compressed in creases across thecorrugations, whereby the structure is flexible by bending of thecorrugated stack at the creases.
 4. A flexible multilayer metalstructure of claim 1 further comprising a third metal sheet interlockedwith the two metal sheets.
 5. A flexible multilayer metal structureaccording to claim 1 further comprising spacers.
 6. The multilayer metalstructure of claim 1, wherein the two metal foil layers are metal foileach having a thickness of 0.005 in. or less.
 7. The multilayer metalstructure of claim 1, wherein the two metal foil layers are metal foileach having a thickness of 0.002 in. or less.
 8. The multilayer metalstructure of claim 1, wherein at least three of the fold regions areparallel.
 9. The multilayer metal structure of claim 2, wherein thespacing between the folds is substantially regular.
 10. A method offorming a flexible multilayer metal structure suitable for use as a heatshield comprising: forming a stack of metal layers, at least two of themetal layers being metal foil layers each having a thickness of 0.006in. or less; interlocking the metal layers to form a number of folds ofthe layers, wherein the interlocking step is such that the folds holdthe layers together, and at least some of the folds extending intonon-edge portions of the multilayer metal structure, and air gaps aredefined in the multilayer structure.
 11. A method according to claim 10wherein the interlocking step comprises forming corrugations across thestack of metal layers whereby the corrugations in the layers are nestedin the stack; and compressing a portion of the corrugations in the stackof metal sheets to form the folds and interlock the layers together. 12.A method according to claim 11 further comprising forming creases acrossthe corrugations to provide flexibility of the structure by bending atthe creases.
 13. A method according to claim 10 wherein the stackcomprises a third metal sheet.
 14. A method according to claim 10wherein the stack further comprises spacers.
 15. A method of making aflexible multilayer metal structure suitable for use as a heat shieldcomprising; providing metal sheets; forming a stack of the metal sheetswhere the stack comprises at least three layers of metal sheets whereinat least two of the layers are metal foil each having a thickness of0.006 in. or less; and interlocking the metal sheets to form a number offolds of the layers, wherein the interlocking step is such that thefolds hold the layers together, and at least some of the folds extendinginto non-edge portions of the multilayer structure, and air gaps aredefined in the multilayer structure.
 16. A method according to claim 15wherein the interlocking step comprises forming corrugations across thestack of metal sheets whereby the corrugations in the layers are nestedin the stack; and compressing a portion of the corrugations in the stackof metal sheets to form folds and interlock the layers together.
 17. Amethod according to claim 16 further comprising forming creases acrossthe corrugations to provide flexibility of the structure by bending atthe creases.
 18. A flexible multilayer metal structure suitable for useas a heat shield comprising: at least two layers of metal sheets eachhaving a thickness greater than 0.006 in.; wherein the two metal layersbeing interlocked together to form a number of folds of the layers, thefolds holding the layers together, at least some of the folds extendinginto non-edge portions of the multilayer metal structure, wherein themultilayer structure defines air gaps that aid in producing a heatshielding effect.
 19. The flexible multilayer metal sheet structureaccording to claim 18 wherein the two layers of metal sheets arecorrugated together in nested corrugations and a portion of thecorrugations are compressed to form interlocking folds of the layers.20. A flexible multilayer metal sheet structure according to claim 18further comprising a third metal sheet interlocked with the two metalsheets.
 21. A flexible multilayer metal sheet structure according toclaim 18 comprising spacers.
 22. A method of forming a flexiblemultilayer structure suitable for use as a heat shield comprising:forming a stack of metal sheets, the metal sheets including at least twometal foil layers each having a thickness of greater than 0.006 in.;interlocking the metal layers to form a number of folds of the layers,wherein the interlocking step is such that the folds hold the layerstogether, and at least some of the folds extending into non-edgeportions of the multilayer metal structure, and air gaps are defined inthe multilayer structure.
 23. A method according to claim 22 wherein theinterlocking step includes forming corrugations across the stack ofmetal sheets whereby the corrugations in the layers are nested in thestack; and compressing a portion of the corrugations in the stack ofmetal sheets to form interlocking folds of the layers.
 24. A methodaccording to claim 23 further comprising forming creases across thecorrugations to provide flexibility of the structure by bending at thecreases.
 25. A method according to claim 22 wherein the stack comprisesa third metal sheet.